The purpose of this study is to determine the effect of dietary protein levels on lifespan of the hamsters will be fed either 6, 12, 18 or 24 percent protein in a pelleted ration. The mean lifespan of each group will be calculated and survivors will be killed when 20 percent of a group remains. All hamsters will be necropsied and the kidneys will be examined histologically for nephritis. Other major organs will also be examined for lesions. Prior to necropsy of survivors, blood pressure will be determined by cannulation of the carotid artery.